Screw conveyor for a bowl centrifuge



Dec. 6, 1966 G. HILLER 3,289,926

SCREW CONVEYOR FOR A BOWL CENTRIFUGE Filed Oct. 14, 1964 ATTORNE YS United States Patent O 3,239,926 SCREW CNVEYR FR A BGWL CENTRIFUGE Georg Hiller, Vilsbiburg, Lower Bavaria, Germany, assignor to lilottweg-Motorenwerli Dr. Georg Bruckmayer, Vilsbiburg, Lower Bavaria, Germany Filed Oct. 14, B64, Ser. No. 403,799 l Claims. (Cl. 233-7) The present invention relates to a bowl centrifuge with a fully closed conical bowl or jacket and a conveying spiral or screw therein which is mounted on and winds around a rotating central hollow shaft through which the material to be centrifuged is supplied and then passed through an inlet opening in the wall of this shaft into the separating chamber between this shaft and the spiral thereon and the inner surface of the rotating jacket.

In centrifuges of this type it is often noticed that even though during a certain length of time after the machine has been in operation the discharged liquid contains Very few, if any, fine solid particles, the amount of such particles in the discharged liquid increases when the machine operates for a greater length of time and the separating efficiency of the centrifuge therefore decreases considerably. This is due to the fact that the ne particles, which are primarily separated in the further part of the centrifuge, are passed by the spiral in the conveying didection toward the discharge opening for the solid substances and thus past the inlet opening for the material to be centrifuged where they are again whirled up by the newly added material. The opening through which the new material is passed into the separating chamber usually lies near the center of the length of this chamber, and the material, and especially the coarse material, en-

ering the chamber is thrown with great force against the wall of the rotating jacket and thereby again whirls up the fine particles which have already been separated so that a circulation of this line material is produced in the separating chamber with the result that the longer the operation continues, the greater will be the rate of concentration of the fine particles in the liquid which is discharged in the direction opposite to the conveying direction of the spiral.

Efforts have already been made to overcome this disadvantage hy adding smaller amounts of new material within a given period of time. However, even though the rate of feeding new material was considerably reduced, the component of ne particles in the discharged liquid still remained practically the same if the operation was continued for a greater length of time.

Other attempts to prevent this disadvantage consisted in providing means between the inlet opening through which the material is supplied in to the separating chamber and the wall of the rotating jacket for preventing the impact of this material upon the wall. However, these efforts were likewise unsuccessful.

It is an object of the present invention to design a centrifuge of the type as above described in a manner so as to insure that the liquid discharged therefrom will be practically free of any ne solid particles even after the machine has been in operation for a longer period of time. According to the invention, this object is attained by providing the pipe carrying the spiral between two adjacent turns thereof with an additional section of a a further spiral at a point near and in front of the inlet opening for the material to be treated, as seen in the conveying direction of the spiral. The effect which is hereby attained is that the fine particles which have already been separated will be deflected from the inlet opening so that this tine material will not be located at the point where the new material to be treated hits upon the wall of the rotating jacket. After having been deflected from and moved past the inlet opening by means 3,2%,925 Patented Dec. 6, i965 of this additional section of a spiral, the line material then passes into the narrower part of the conical jacket in which the coarser material settles and from which it is then expelled together with the latter.

Another feature of the invention consists in considerably increasing the pitch of the spiral, preferably to twice its normal size, within the area adjacent to the inlet opening, whereasthe additional spiral section has a pitch corresponding to that of the main spiral in front of and behind the inlet opening.

The additional spiral section preferably extends along an angular distance of about to 250 and preferably about The main spiral as well as the additional spiral section may also have a double or multiple thread.

The features of the invention will become more clearly apparent from the following description of the accompanying ydrawing of the central part of the conveying spiral of a full-jacket centrifuge according to the invention.

In the drawing, the screw conveyor comprises the conveying spiral or screw 1 of the centrifuge, which is mounted on and rotatable with a central hollow pipelike shaft 1' and it is surrounded by a conical jacket, not shown, which is likewise rotatable. The slurry to be centrifuged is supplied through the shaft 1 and passes through an inlet opening 2 in the wall of this shaft 1 into the separating chamber which is limited toward the outside by the conical jacket. Between two adjacent turns of the spiral 1 a section 3 of a turn of an additional spiral is secured to the shaft 1 at a point in front of the inlet opening 2, as seen in the conveying direction of the spiral from the right toward the left of the drawing. Within the area adjacent to the inlet opening 2 the pitch of the spiral 1 is considerably increased, while the additional spiral section or deflector plate has a pitch substantially corresponding to that of the parts of the spiral 1 outsi-de of the area of the inlet opening 2.

By means of the additional spiral section 3, the line particles which have already been separated will be deilected away from the area directly between the inlet opening 2 and the wall of the conical jacket and will be carried to a point beyond the inlet opening. They will thus not be stirred up by the new material entering through the inlet opening 2 and hitting against the wall of the jacket but will be taken along with the coarser material in the conveying direction of the spiral towar-d the left of the drawing, while the liquid runs off in the opposite direction.

The further part of the centrifuge is that part of the centrifuge where the diameter of the spiral is greater than the diameter of the spiral in the plane of the inlet opening.

Although my invention has been illustrated and described with reference to the preferred embodiment thereof, I wish to have it understood that it is in no w'ay limited to the details of such embodiment, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

1. A screw conveyor, comprising a rotatable hollow shaft having an inlet opening in its walls, a substantially helical conveying screw secured for rotation with said shaft, said inlet opening being located between adjacent turns of said conveying screw, a generally radially extending deector plate means secured for rotation to said shaft axially spaced from said inlet opening between said inlet opening and an adjacent turn of said conveying screw, and said deilector plate means being operable to deflect the conveyed material away from said inlet open- 2. The screw conveyor of claim 1, wherein said defiector plate means has an angular extent between 120 to 250 around the periphery of said shaft.

3. The screw conveyor of claim 1, wherein said deector plate means has an angular extent of substantially 180 around the periphery of said shaft.

4. The screw conveyor of claim 1, wherein said adjacent turns of said conveying screw having a pitch substantially larger than the normal pitch of said conveying screw in front of and behind said adjacent turns.

5. The screw conveyor of claim 4, wherein said deector plate means has an angular extent of substantially 180 aroun-d the periphery of said shaft.

6. The screw conveyor of claim 1, wherein the pitch between said adjacent turns of said conveying screw is substantially twice as large as the normal pitch of said conveying screw in front of and behind said adjacent turn, and wherein said deflector plate means is la helical section having a pitch substantially equal to said normal pitch.

7. The screw conveyor of claim 6, wherein said deector plate means has an angular extent substantially 180 around the periphery of said shaft.

8. The screw conveyor of claim 1, wherein said conveying screw extends radially outward from said shaft a distance that progressively and continuously decreases in one axial direction in the vicinity of said inlet opening.

9. The screw conveyor of claim 8, wherein said deector plate means has an angular extent of substantially 180 around the periphery of said shaft.

l0. The screw conveyor of claim 8, wherein said adjacent turns of said conveying screw have a pitch substantially larger than the normal pitch of said conveying screw in front of and behind said adjacent turns.

11. The screw conveyor of claim 10, wherein said inlet opening is spaced from said deflector plate means in said one axial direction.

12. The screw conveyor of claim 8, wherein the pitch between said adjacent turns of said conveying screw is substantially twice as large as the normal pitch of said conveying screw in front of and behind said adjacent turn, and wherein said deflector plate means is a helical section having a pitch substantially equal to said normal pitch. y

13. The screw conveyor of claim 12, wherein said inlet opening is space-d from said deflector plate means in said one axial direction.

14. The screw -conveyor of claim 8, wherein said inlet opening is spaced from said deectorplate means in said one axial direction.

15. The screw conveyor of claim 14, wherein said detlector plate means has an angular extent of substantially around the periphery of said shaft.

References Cited by the Applicant UNITED STATES PATENTS 775,320 11/ 1904 Van Kirkf. 1,383,313 '7/1921 Landreth. 3,098,820 7/ 1963 Gooch.

M. CARY NELSON, Primary Examiner.

H. KLINKSIEK, Assistant Examiner. 

1. A SCREW CONVEYOR, COMPRISING A ROTATABLE HOLLOW SHAFT HAVING AN INLET OPENING IN ITS WALLS, A SUBSTANTIALLY HELICAL CONVEYING SCREW SECURED FOR ROTATION WITH SAID SHAFT, SAID INLET OPENING BEING LOCATED BETWEEN ADJACENT TURNS OF SAID CONVEYING SCREW, A GENERALLY RADIALLY EXTENDING DEFLECTOR PLATE MEANS SECURED FOR ROTATION TO SAID SHAFT AXIALLY SPACED FROM SAID INLET OPENING BETWEEN SAID INLET OPENING AND AN ADJACENT TURN OF SAID CONVEYING 